Abstract

Growht anomalies on linden trees related to their decline in Quebec : needs to apply preventive measures in the early life of the tree

Since 1993, a pronounced decline in the health condition of linden trees (mainly from Tilia cordata Mill. lineage) has been responsible for the removal of 5% of the total planted linden trees in Quebec City (Quebec, Canada). Among the various growth anomalies observed on these trees, numerous gall-like outgrowths developing on the trunks and pronounced swellings at the base have appeared to be preponderant factors leading to decline. These anomalies have favoured the action of secondary agents such as opportunistic insects and microorganisms, and of damaging disturbances, such as a pronounced fissuring and cracking of the bark, bark peeling, and so on. Analysis of disks eut from 30 felled trees has shown that the anomalies had originated at the centre of the tree, and that their growth and effect had started to increase rapidly several years ago. The results of surveys conducted on more than 900 recently planted linden trees in Quebec City and elsewhere indicate that such outgrowths on the stem as well as the swellings at the tree base were present on a large number of the trees and were starting to expand, but with marked differences between varieties. These data point to the necessity of developing preventive measures and applying them early in the tree life to prevent such anomalies.